1. Field of the Invention
This invention relates to a quartz oscillation-type electronic timepiece, and more specifically to a quartz oscillation-type electronic timepiece employing a quartz oscillator as a time reference source and employing a logic circuit consisting of complementary MOS transistors (hereinafter abbreviated as CMOST's) having means for dividing the frequency of the oscillator to a value suited for the time display means. If mentioned in further detail, the present invention relates to an electronic timepiece equipped with a constant-voltage circuit which is capable of eliminating voltage fluctuation that results from a battery of the type that permits the discharge voltage to vary from 1.8 volts to 1.55 volts, such as silver peroxide battery.
2. Description of the Prior Art
A silver battery has heretofore been used as an energy source for wrist watches. In recent years, a silver peroxide battery was developed as a new silver battery. As compared with the conventional batteries, the silver peroxide battery stores about 50% more energy per unit volume and, hence, features extended serviceable battery life. The silver peroxide battery has an initial voltage of as high as 1.8 to 1.85 volts.
FIG. 1 illustrates discharge characteristics of the silver peroxide battery and of a conventional silver battery, wherein a solid line (a) represents discharge characteristics of the conventional silver battery having a voltage maintained at about 1.55 volts. A broken line (b), on the other hand, represents discharge characteristics of the silver peroxide battery. It will be obvious that the silver peroxide battery exhibits increased voltage variation.
If the silver peroxide battery storing increased amount of energy per unit volume is used for a quartz oscillation-type electronic timepiece which is shown in FIG. 2, a large voltage variation affects the oscillation frequency of the quartz oscillator and deteriorates the precision of the timepiece. Namely, when the battery is renewed, if the pace of the oscillation frequency is corrected by means of a trimmer capacitor or the like, gradual drop in the battery voltage causes the frequency to be shifted by several ppm relative to the initial condition. Therefore, the difference in frequency from the initially set value is accumulated, giving rise to the occurrence of error in the time display.
FIG. 2 is a block diagram of a conventional timepiece which consists of an oscillation unit 1, a frequency-dividing unit 2, a display drive unit 3, and a time display device 4. A silver peroxide battery 7 which is a power supply feeds a constant voltage to the electronic circuit units. With the thus constructed conventional timepiece, however, voltage variation of the silver peroxide battery causes the oscillation frequency to become out of order and decreases the precision of the timepiece.